New Study: Marijuana’s Impact on Adolescents’ Cognitive Functioning “Overstated”

The study found that cannabis exposure is not associated with any significant long-term adverse cognitive performance effects.

New research investigating the effects of heavy cannabis use on cognitive functioning in adolescents and young adults has found little to no long-term harm. According to the new literature review published in the journal JAMA Psychiatry, any cognitive deficits associated with marijuana use diminish after three days of abstinence.

Researchers from the University of Pennsylvania, Perelman School of Medicine, and the Children’s Hospital of Pennsylvania reviewed the data on young people and cannabis use from 69 separate studies published between 1973 and 2017. The combined data allowed the investigators to compare results among 2,152 frequent marijuana users to 6,575 non-users.

The meta-analysis did find significantly lower scores in various cognitive domains – including learning, abstraction, speed of processing, delayed memory, inhibition, and attention — in teens and young adults that identified as heavy marijuana users.

When researchers separated the studies based on length of abstinence from marijuana, however, the difference in cognitive functioning between marijuana users and non-users were no longer apparent after users had abstained from cannabis for 72 hours.

“[A]bstinence of longer than 72 hours diminishes cognitive deficits associated with cannabis use,” the study concluded.

“[R]esults indicate that previous studies of cannabis youth may have overstated the magnitude and persistence of cognitive deficits associated with marijuana use.”

Full text of the entire study is available to access through JAMA Psychiatry.

teens marijuana effects

Teens and Cannabis

The JAMA Psychiatry study is the latest in a growing body of evidence indicating that cannabis use by teens is not independently linked to adverse cognitive performance.

Last year, a longitudinal co-twin control study found that marijuana use alone wasn’t linked with negative changes in intelligence quotient (IQ) or executive functioning. Instead, family background was found to be associated with adverse cognitive performance in teens. The year prior, researchers found no link to cannabis use and declines in IQ in 3,066 twin teens over an eight-year period.

“These findings, combined with other recent studies reporting that cannabis exposure appears to have minimal adverse impact on brain morphology — particularly when compared to the dramatic effects of alcohol —dispute the long-standing ‘stoner-stupid’ stereotype,” said NORML Deputy Director Paul Armentano in response to the latest study’s conclusions.

As legalization of recreational and medical marijuana continues to expand throughout the United States, these research findings may help further ease concerns of those opposed to policy changes because of the belief that legalizing could adversely impact young people.

“These findings should help to assuage fears that cannabis’ acute effects on behavior may persist long after drug ingestion, or that they may pose greater potential risks to the developing brain,” Armentano added.

Multiple studies have also found that the loosening of cannabis laws does not encourage teens to use marijuana, make it easier for them to obtain marijuana, or cause them to start using cannabis earlier in their lives. While marijuana is legal in some capacity in nearly 30 states, the rate of cannabis use among teens is at a 22-year low.

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